Re: [PATCH v3 4/5] xen: Add files needed for minimal riscv build

[Connor Davis <connojdavis@xxxxxxxxx>]

On 5/17/21 7:43 PM, Bob Eshleman wrote:
> On 5/14/21 4:47 PM, Connor Davis wrote:
> > On 5/14/21 3:53 PM, Bob Eshleman wrote:
> > > On 5/14/21 11:53 AM, Connor Davis wrote:
> > >
> > > > +
> > > > +#ifdef CONFIG_RISCV_64
> > > > +
> > > > +/*
> > > > + * RISC-V Layout:
> > > > + *   0x0000000000000000 - 0x0000003fffffffff (256GB, L2 slots [0-255])
> > > > + *     Unmapped
> > > > + *   0x0000004000000000 - 0xffffffbfffffffff
> > > > + *     Inaccessible: sv39 only supports 39-bit sign-extended VAs.
> > > > + *   0xffffffc000000000 - 0xffffffc0001fffff (2MB, L2 slot [256])
> > > > + *     Unmapped
> > > > + *   0xffffffc000200000 - 0xffffffc0003fffff (2MB, L2 slot [256])
> > > > + *     Xen text, data, bss
> > > > + *   0xffffffc000400000 - 0xffffffc0005fffff (2MB, L2 slot [256])
> > > > + *     Fixmap: special-purpose 4K mapping slots
> > > > + *   0xffffffc000600000 - 0xffffffc0009fffff (4MB, L2 slot [256])
> > > > + *     Early boot mapping of FDT
> > > > + *   0xffffffc000a00000 - 0xffffffc000bfffff (2MB, L2 slot [256])
> > > > + *     Early relocation address, used when relocating Xen and later
> > > > + *     for livepatch vmap (if compiled in)
> > > > + *   0xffffffc040000000 - 0xffffffc07fffffff (1GB, L2 slot [257])
> > > > + *     VMAP: ioremap and early_ioremap
> > > > + *   0xffffffc080000000 - 0xffffffc13fffffff (3GB, L2 slots [258..260])
> > > > + *     Unmapped
> > > > + *   0xffffffc140000000 - 0xffffffc1bfffffff (2GB, L2 slots [261..262])
> > > > + *     Frametable: 48 bytes per page for 133GB of RAM
> > > > + *   0xffffffc1c0000000 - 0xffffffe1bfffffff (128GB, L2 slots [263..390])
> > > > + *     1:1 direct mapping of RAM
> > > > + *   0xffffffe1c0000000 - 0xffffffffffffffff (121GB, L2 slots [391..511])
> > > > + *     Unmapped
> > > > + */
> > > > +
> > > What is the benefit of moving the layout up to 0xffffffc000000000?
> > I thought it made the most sense to use the upper half since Xen is privileged
> >
> > and privileged code is typically mapped in the upper half, at least on x86. I'm 
> > happy to
> >
> > move it down if that would be preferred.
> I do like the idea of following norms, but I think I prefer following the ARM 
> norm
> over the x86 norm unless there is a technical reason not to. Just due to
> ARM and RISC-V having much more overlap than x86 and RISC-V.  In this case,
> all things being equal, I'd prefer following the ARM model and use the lower 
> half.
> I definitely like adding the note on the inaccessible region.
Sounds good, I will move it down.


Thanks,

Connor